350 THE BOOK OF A NATURALIST 
down in this dark dead soil the worms will insist 
on descending, although their only way to it is 
through the few small cylindrical holes they have 
succeeded in boring through the partially rotted 
cement between the tiles, or where a minute stone 
has dropped out of the tesserae pavements. Their 
descent into these difficult places and down into 
the old pits involves long double journeys daily 
when they are forced to come up to deposit their ~ 
castings on the surface. 
What then is the force impelling them? Why 
do they leave a rich feeding-ground for a poor one? 
I take these facts in their relation to other well- 
known facts, as for example that of the quite 
extraordinary difference in size and vigour and 
colouring in the earthworms inhabiting different 
soils. They are like different species. Let us take 
the case of the London earthworm to be found in 
every few square yards of earth unbuilt on, even 
in the very heart of the City itself. Judging from 
all the specimens I have examined, this worm 
attains to about half the full normal size and is 
comparatively languid in his movements and rarely 
exhibits the brilliant play of colours seen in the 
large country worm in rich soil—the colour which 
is the sign of intensity of life. Doubtless he was 
once a big vigorous worm, but that was long ago 
in an old London, or Londineum, and he has had 
ample time to degenerate. In this state he is now 
biding his time, under our feet, and his time will 
come when our seven millions have faded or 
